Field-tuned collapse of an orbitally ordered and spin-polarized state:: Colossal magnetoresistance in the bilayered ruthenate Ca3Ru2O7 -: art. no. 014404

Ca3Ru2O7 with a Mott-like transition at 48 K and a Neel temperature at 56 K features different in-plane anisotropies of the magnetization and magnetoresistance. Applying a magnetic field along the magnetic easy-axis precipitates a spin-polarized state via a first-order metamagnetic transition, but does not lead to a full suppression of the Mott state, whereas applying a magnetic field along the magnetic hard axis does, causing a resistivity reduction of three orders of magnitude. The colossal magnetoresistivity is attributed to the collapse of an orbitally ordered and spin-polarized state. This phenomenon is striking in that the spin polarization, which is a fundamental driving force for all other magnetoresistive systems, is detrimental to the colossal magnetoresistence in this 4d-based electron system. Evidence of a density wave is also presented.